Western Australian Grain Belt Research Articles

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

Growers’ perceptions and attitudes towards fungicide resistance extension services

Agricultural extension services have been successful in promoting knowledge sharing and innovation in agriculture. However, the adoption of new agricultural practices, particularly in integrated pest management, has been slow. Using a case study with a co-designed survey instrument, this research aimed to understand how growers in the Southwest Western Australian Grainbelt access information and resources to manage fungicide resistance. We found that the growers rely on a combination of paid agronomists, government or research institutes, local grower groups, and field days for fungicide resistance information. Growers seek information from trusted experts who can simplify complex research, value easy-to-understand communication and prefer resources tailored to their local context. Additionally, growers valued information regarding new fungicide developments and having access to rapid fungicide resistance diagnostic services. These findings highlight the importance of providing growers with effective agricultural extension services to manage the risk of fungicide resistance.

Early silique-shedding wild radish (Raphanus raphanistrum L.) phenotypes persist in a long-term harvest weed seed control managed field in Western Australia.

This study introduces a wild radish population collected from Yelbeni in the Western Australian grainbelt that evolved an early silique abscission (shedding) trait to persist despite long-term harvest weed seed control (HWSC) use. In 2017, field-collected seed (known herein as Yelbeni) was compared to surrounding ruderal and field-collected populations in a fully randomized common garden study. The Yelbeni population exhibited a higher rate of silique abscission when compared to the ruderal populations collected from the site before wheat (Triticum aestivum L.) harvest (assessed at soft dough stage, Zadoks 83). A similar common garden study was conducted in the subsequent season (2018) using progeny reproduced on a single site without stress. The HWSC-selected progeny (Yelbeni P) shed 1048 (±288) siliques before wheat maturity at the soft dough stage (Zadoks 83) compared to 25 (±7) siliques from the pooled control populations. The Yelbeni P population only flowered 6 days earlier (FT50 as determined by log-logistic analysis) than pooled control populations, which is unlikely to fully account for the increased rate of silique abscission. The Yelbeni P population also located its lowest siliques below the lowest height for harvest interception (10 cm), which is likely to increase HWSC evasion. The mechanism inducing early silique-shedding is yet to be determined; however, wild radish is known for its significant genetic variability and has demonstrated its capacity to adapt to environmental and management stresses. This study demonstrates that the repeated use of HWSC can lead to the selection of HWSC-avoidance traits including early silique-shedding before harvest and/or locating siliques below the harvest cutting height for interception. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Concurrent evolution of seed dormancy and herbicide resistance in field populations of dominant weed species in Western Australian cropping systems

AbstractHerbicide resistance, documented in many economically damaging weed species, is a major threat to global crop production. The injudicious use of herbicides, often in the absence of diverse weed control strategies, poses an immense selection pressure on weed communities for resistance evolution and weed adaptive traits such as high seed dormancy. This study evaluates the interaction among developing herbicide resistance, seed size, and seed dormancy of ripgut brome (Bromus diandrus Roth), wild oat (Avena fatua L.), and hare barley [Hordeum leporinum Link; syn. Hordeum murinum L. ssp. leporinum (Link) Arcang.] collected from within intensively managed fields (in-crop) in comparison with populations in surrounding ruderal (non-crop disturbed) areas with no history of exposure to herbicides within the Western Australian grainbelt. Seed size of the three species varied by farming system (continuous cereal-intensive annual crops, diverse annual crops, pasture based) and habitat (in-crop, ruderal). Field populations of H. leporinum and B. diandrus tended to have greater seed size compared with ruderal populations. Larger seeds had significantly more dormancy in all three weed species. Field-collected populations that were exposed to herbicide applications for at least the past 5 yr exhibited significantly greater seed dormancy compared with their counterparts present in ruderal areas within the same geographic area. The association between increased seed dormancy and developing multiple herbicide resistance further complicates effective weed management.

Identification of the first glyphosate-resistant capeweed (Arctotheca calendula) population.

Glyphosate is routinely used in Australia to control the Arctotheca species Arctotheca calendula (L.) Levyns (referred hereinafter as capeweed). This study identifies the first global case of field-evolved glyphosate-resistant capeweed, collected from the grainbelt of Western Australia. In 2020, a capeweed biotype that was collected from Borden in the southern Western Australian grainbelt was confirmed to be glyphosate-resistant (referred hereinafter as Spence population). When compared to the pooled mortality of six field-collected, glyphosate susceptible capeweed populations (S1, S2, S3, S4, S5 and S6), the Spence population was found > 11-fold more resistant to glyphosate than the pooled results of the susceptible populations (S1-S6) at the lethal dose of 50% (LD50 ) level. The growth of the Spence population was also less affected, requiring > 13-fold more glyphosate to reduce growth than the pooled susceptible populations at the growth reduction of 50% (GR50 ) level. Sequencing of the plastidic 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene indicated no known single gene mutation imparting glyphosate resistance. This study, however, did not investigate any other known mechanisms that impart glyphosate resistance. When screened at the field-applied rate, this Spence population was also found to survive an inhibitor of acetolactate synthase (ALS) (metosulam) and an inhibitor of phytoene desaturase (diflufenican). This is the first confirmation of glyphosate resistance evolution in a capeweed population globally. With capeweed resistance already confirmed to photosystem-I inhibiting herbicides (paraquat and diquat), this study emphasizes the importance of using integrated measures that do not depend only on the use of non-selective herbicides for controlling herbicide resistance-prone capeweed populations. © 2021 Society of Chemical Industry.

Summer weed species incidence in Western Australia varies between seasons

AbstractAgronomic surveys of summer weed species are necessary to identify future research directions for optimal weed control, but usually focus on agricultural fields in a single season. To survey all species in the absence of weed control measures and determine species variability between seasons, a survey of 133 sites was conducted on roadsides adjoining agricultural fields throughout the Western Australian grainbelt in early 2015 and repeated in 2016 and 2017. The survey identified 144 species, but only 19 species were evident at more than 10% of sites. The most common species were weeping lovegrass [Eragrostis curvula (Schrad.) Nees], fleabane (Erigeron sp.), windmillgrass (Chloris truncata R. Br.), and wild radish (Raphanus raphanistrum L). The survey highlighted that weed species incidence varied between years. For example, C. truncata incidence was 30% in 2015 and 55% in 2016, while stinkgrass [Eragrostis cilianensis (All.) Vignolo ex Janch.] ranged from 20% in 2015 to 50% of sites in 2017. Conversely, density of individual species on the roadside was usually low, and density remained consistent between years. The survey highlighted multiple weed species that will require further research to optimize management programs. Raphanus raphanistrum and wild oat (Avena fatua L.) in particular are an issue for growers, as these species are highly detrimental winter weeds, and the survey demonstrates that they can also be common summer weeds. Control of these species with nonselective herbicides in summer as well as winter is likely to exacerbate the development of herbicide resistance.

Quantifying the spatial pattern of the yield gap within a farm in a low rainfall Mediterranean climate

Quantification of the gap between water-limited yield and actual crop yields at a sub-field scale across grain farms are now becoming possible in industrialised agriculture because of routine yield mapping and readily available methods to estimate potential yield. Analyses at sub-field scale can be used to target intervention strategies such as matching fertiliser inputs to yield variation or amelioration of soil constraints. As such they complement the predominant “top-down” approaches to the quantification of yield gaps and are relevant to individual farm decision making. In this study we bring together yield maps, farm soil surveys, and rainfall records to generate whole-farm maps of actual yield, water-limited potential yield, the yield gap, the contribution of soil constraints to the yield gap, and a list of the feasible interventions to close that gap. We apply the approach in a case study of a 4500ha rainfed farm, located in the low-rainfall cropping zone of the Western Australian grainbelt. We found a substantial gap between water-limited potential yield and actual yield, in an environment where wheat yields typically range between 0.5 and 2.5t/ha. On a whole-of-farm basis, mean wheat yield was 50–60% of the water-limited yield and the yield gap varied from 0.6t/ha in a dry year to 1.5t/ha in wet year. The size of the yield gap varied among and within soil types due to associated soil constraints, and the analysis suggested that addressing the predominant constraint of acidity on the average performing areas on the farm could generate the greatest gains, rather than focussing on the below-average areas that have large yield gaps, which are afflicted by intractable soil constraints.The approach can be used by advisors and farmers to assess the proportion of the farm that reaches attainable or water-limited yield, and a tool to target regions within the farm that fail to reach attainable yield. This style of analysis lends itself to landscapes where there is a strong association between crop yield and soil type and environments where yield is strongly determined by rainfall and hence water-limited yield can be easily calculated. With an increase in the routine use of yield monitors by grain growers we anticipate an increase in yield map coverage across farms that will eventually make our method readily applicable.

Domestication bottlenecks limit genetic diversity and constrain adaptation in narrow-leafed lupin (Lupinus angustifolius L.)

In contrast to most widespread broad-acre crops, the narrow-leafed lupin (Lupinus angustifolius L.) was domesticated very recently, in breeding programmes isolated in both space and time. Whereas domestication was initiated in Central Europe in the early twentieth century, the crop was subsequently industrialized in Australia, which now dominates world production. To investigate the ramifications of these bottlenecks, the genetic diversity of wild (n = 1,248) and domesticated populations (n = 95) was characterized using diversity arrays technology, and adaptation studied using G × E trials (n = 31) comprising all Australian cultivars released from 1967 to 2004 (n = 23). Principal coordinates analysis demonstrates extremely limited genetic diversity in European and Australian breeding material compared to wild stocks. AMMI analysis indicates that G × E interaction is a minor, albeit significant effect, dominated by strong responses to local, Western Australian (WA) optima. Over time Australian cultivars have become increasingly responsive to warm, intermediate rainfall environments in the northern WA grainbelt, but much less so to cool vegetative phase eastern environments, which have considerably more yield potential. G × E interaction is well explained by phenology, and its interaction with seasonal climate, as a result of varying vernalization responses. Yield differences are minimized when vegetative phase temperatures fully satisfy the vernalization requirement (typical of eastern Australia), and maximized when they do not (typical of WA). In breeding for WA optima, the vernalization response has been eliminated and there has been strong selection for terminal drought avoidance through early phenology, which limits yield potential in longer season eastern environments. Conversely, vernalization-responsive cultivars are more yield-responsive in the east, where low temperatures moderately extend the vegetative phase. The confounding of phenology and vernalization response limits adaptation in narrow-leafed lupin, isolates breeding programmes, and should be eliminated by widening the flowering time range in a vernalization-unresponsive background. Concomitantly, breeding strategies that will widen the genetic base of the breeding pool in an ongoing manner should be initiated.

Herbicide-Resistant Weed Seeds Contaminate Grain Sown in the Western Australian Grainbelt

Preventing the introduction of weeds into the farming system through sowing of clean seeds is an essential component of weed management. The weed seed contamination of cleaned grain and herbicide resistance levels of the recovered weed seeds were examined in a study conducted across 74 farms in the Western Australian grainbelt. Most farmers grew and conserved their own crop seed. The majority of cleaned samples had some level of seed contamination from 11 foreign weed and volunteer crop species, with an average of 62 seeds 10 kg−1grain, substantially higher than the 28 seeds 10 kg−1grain expected by farmers. The most common weed contaminants across all samples were rigid ryegrass, wild radish, brome, and wild oat. When categorized by crop type, rigid ryegrass was the most frequent contaminant of cereal crops (barley and wheat), however wild radish was the most frequent contaminant of lupin crops. Uncleaned crop seed samples had almost 25 times more contamination than cleaned crop seed. Herbicide resistance was highly prevalent within rigid ryegrass populations recovered from cleaned grain except for glyphosate, which controlled all populations tested. Some resistance was also found in wild radish and wild oat populations; however, brome was susceptible to fluazifop. This study has shown that farmers are unknowingly introducing weed seeds into their farming systems during crop seeding, many of which have herbicide resistance.

Aphid feeding damage causes large losses in susceptible lupin cultivars

The impact of infestation by bluegreen aphid, Acyrthosiphon kondoi, cowpea aphid, Aphis craccivora, and/or green peach aphid, Myzus persicae, on grain production of narrow-leafed lupin (Lupinus angustifolius) and yellow lupin (Lupinus luteus) was assessed at 4 sites in the Western Australian grainbelt. Yield losses caused by naturally occurring aphids on 4 cultivars of narrow-leafed and 2 cultivars of yellow lupins were measured by applying the systemic insecticide imidacloprid as a seed dressing and/or as foliar sprays throughout the plant growth phase and compared with untreated control plots. The extent of damage caused by aphids varied greatly but was significantly influenced by lupin cultivar, and yields for the same treatment combination varied between geographical locations. Bluegreen aphid was the most abundant species wherever large colonies of aphids developed. Yellow lupin Wodjil was the most infested and suffered severe losses in grain yield, whereas narrow-leafed lupin Kalya was largely resistant to aphids and there were negligible losses in grain production from plots not treated for aphids. In a fifth experiment, a single foliar spray of the insecticide pirimicarb controlled abundant aphids and increased yield by as much as 95% (0.65 t/ha) in Wodjil. Lupin growers need to be aware of the potential losses aphids can cause and that applying foliar insecticidal sprays to susceptible cultivars can prevent such losses.

An autecological study of the take-all fungus (Gaeumannomyces graminis var. tritici) in Western Australia

The Western Australian (W.A.) grainbelt has a mediterranean-type climate, with hot-dry summers and mild-wet winters, and this together with the old, and often nutritionally poor, sandy acidic soils has determined the nature of the agricultural system of the region. Wheat is the major crop, and take-all disease is a serious problem which is exacerbated both by the climatic and edaphic conditions and the prevailing agricultural practices.The behaviour of the inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici) in W.A. is markedly different from that reported from cool-temperate regions and therefore the disease requires different control strategies. Although relationships between inoculum and disease have been studied in W.A., the potential use of inoculum status of field soil for disease prediction is limited by the lack of predictability of rainfall.

Pectic zymograms and taxonomy and pathogenicity of the Ceratobasidiaceae

The pectic enzymes of 140 isolates of Rhizoctonia-1ike fungi from the Western Australian grainbelt were examined by electrophoresis and found to fall into 11 distinct zymogram groups (ZG). Isolates within a ZG had a similar cultural and morphological appearance and were either all multinucleate or all binucleate. Some isolates from most ZGs sporulated when transferred from potato-dextrose-marmite agar to water agar. Isolates from within a ZG had the same teleomorph. Pathogenicity of the isolates was tested against wheat and lupins. All isolates from within a ZG were consistent in the type of lesions they produced and in their virulence towards these hosts. Rhizoctonia patch disease of cereals and lupins appears to be caused by isolates from ZG 1 and ZG 2. Severe reddish-brown and brown hypocotyl rots of lupins were caused by ZG 3 and ZG 4 isolates respectively. Five Ceratobasidium groups (CZG), one Waitea group (WZG) and ZG 5 had weak to nil pathogenicity towards wheat and lupins.